Regional Anatomy II_Week 9_SU22 PDF

Week 9 Temporomandibular joint, muscles of mastication, mimetic muscles Temporomandibular Joint ● Synovial hinge joint established in the mandibular fossa between the articular tubercle of temporal bone and head of mandible (mandibular condyle) ○ ○ ○ ● ● Mandibular condyle Articular disc Artic...

Week 9 Temporomandibular joint, muscles of mastication, mimetic muscles Temporomandibular Joint ● Synovial hinge joint established in the mandibular fossa between the articular tubercle of temporal bone and head of mandible (mandibular condyle) ○ ○ ○ ● ● Mandibular condyle Articular disc Articular tubercle of temporal bone Articular disc - oval plate of fibrous tissue located between temporal and mandibular articular surfaces separates joint into superior and inferior compartments. It attaches to joint capsule and receives attachment of fibers of lateral pterygoid muscle. It moves forward and backward with mandibular condyle. Articular capsule - surrounds joint like a sleeve Temporomandibular Joint Ligaments: ● ● ● Lateral temporomandibular ligament - strengthens lateral aspect of the joint capsule. Fibers pass inferior and posterior to the neck of the mandible which limits posterior and inferior displacement of mandibular condyle. Sphenomandibular ligament - lies medial to, and separate from, the joint capsule and extends from spine of the sphenoid to lingula of mandibular foramen Stylomandibular ligament - lies posterior/inferior to and separate from joint capsule. It is a thickening of parotid fascia that extends from styloid process to posterior border of ramus of mandible Temporomandibular Joint ● ● Nerve supply is derived from branches of mandibular nerve (V3) via the auriculotemporal (main) and masseteric nerves Blood supply is from branches of superficial temporal and maxillary arteries Temporomandibular Joint ● Movement occurs in three planes ○ ○ ○ Elevation and depression Protraction and retraction Right and left lateral excursion Muscles of Mastication ● ● ● ● ● ● Buccinator Masseter Temporalis Medial pterygoid Lateral pterygoid All muscles are innervated by branches of V3 Masseter Origin: Inferior border and medial surface of zygomatic bone and zygomatic arch Insertion: lateral surface of ramus and angle of mandible Nerve supply: masseteric nerve Main action: elevation of the mandible (bilateral contraction) Temporalis Origin: floor of temporal fossa (some fibers also originate from temporal fascia) Insertion: tendon passes medial to zygomatic arch and inserts into coronoid process and anterior border of ramus of mandible Nerve supply: deep temporal nerves (anterior and posterior) Action: elevate mandible (bilateral contraction) and retrusion of mandible (bilateral contraction of posterior fibers) Medial Pterygoid Origin: ● ● Deep head - medial surface of lateral pterygoid plate Superficial head - tuberosity of maxilla Insertion: medial surface of ramus of angle of mandible Nerve supply: medial pterygoid nerve Action: elevate mandible and laterally deviate it to the opposite side Lateral Pterygoid Origin: ● ● Superior head - infratemporal surface of greater wing of sphenoid Inferior head - lateral surface of lateral pterygoid plate Insertion: Most fibers insert into pterygoid fovea (small depression on anterior aspect of neck of mandible). Some fibers insert into anteromedial aspect of capsule and articular disc of temporomandibular joint. Nerve supply: Lateral pterygoid nerve Action: Depresses and protracts mandible to open mouth. Pulls forward cartilage of the joint during opening of the mouth and aids in chewing. Clinical Considerations ● TMJ disorders affect ~25% of the population at some point in their lives ○ ○ ○ ○ ● TMJ Syndrome - Temporomandibular joint disorder, unspecified- M26. 60 Traumatic causes include sports, vehicular accidents, and fall injuries Dislocation and dental work may also cause TMJ disorders Masseter spasm and tension based clenching Higher in females 4:1 TMJ Dislocation Superior dislocation, aka central dislocations, can occur from a direct blow with to a partially opened mouth. The angle of the mandible in the position predisposes upward migration of the condylar head. This can result in fracture of the glenoid fossa with mandibular condyle dislocation into the middle skull base. Further injuries from the type of dislocation can range from facial nerve injury, to intracranial hematomas, cerebral contusion, leakage of CSF, and damage to CNⅧ, resulting in deafness TMJ Dislocation Anterior dislocation is atraumatic and commonly follows extreme opening of the mouth, such as yawning, dental treatment, eating, etc. Dislocation stretches the ligaments of the masseter, medial and lateral pterygoids, and temporalis muscles, causing painful spasms (trismus). This prevents the condyle from returning to the mandibular fossa. TMJ Dislocation Posterior dislocation typically occurs secondary to a direct blow to the chin. The mandibular condyle is pushed posterior to the mastoid. Injury to the external auditory canal from the condylar head may occur from the type of injury. TMJ Dislocation Lateral dislocations are usually associated with mandible fractures. The condylar head migrates laterally and superiorly and can often be palpated in the temporal space. TMJ Dislocation ● ● ● ● ● Dislocation stretches the ligaments of the masseter, medial and lateral pterygoids, and temporalis muscles, causing painful spasms (trismus). This prevents the condyle from returning to the mandibular fossa. More often bilateral and associated with malocclusion of the teeth Unilateral anterior dislocations will deviate away from the dislocated side May be associated with sensory changes of the CNⅤ distribution Manual reduction with analgesia and sedation is effective for acute dislocation Myofascial Pain Dysfunction Syndrome ● ● MPD, not primarily a joint problem. It results from a chronic muscle tension and sometimes spasm seen with jaw clenching and teeth grinding (bruxism) Primary problem is within the joint itself ○ ○ ● May be a poor positioning of the articulating disc secondary to hypoplastic mandibular condyles or laxity of ligaments Degenerative joint disease Pain along the mandibular branch (V3) of the trigeminal nerve distribution, including: ○ ○ Local capsule Face regions with sensory innervation from V3, roughly the lower ⅓ of the face, including the lower teeth, skin of the chin, and scalp Myofascial Pain Dysfunction Syndrome Common symptoms ● ● ● ● ● ● Pain in the muscles of mastication Radiating pain to the ear and/or jaw Clicking or popping, or locking of the jaw when opening Headache and/or neck pain with or without local joint pain Non-occlusive bite Bruxism Myofascial Pain Dysfunction Syndrome Physical findings: ● ● ● ● ● ● Limited mouth opening Palpable muscle spasm Facial swelling Audible clicking/popping TMJ tenderness to palpation Lateral deviation of mandible Mimetic Muscles Muscle of the Face ● ● ● Embedded in the superficial fascia of the face Originate from the bones of the skull and insert into the skin Serve as sphincters or dilators of facial openings and move overlying skin to modify expression of face Muscle of the Face Muscles of the orbit: ● Orbicularis oculi - sphincter muscle of the eyelids. Palpebral part (centrally located) lightly approximates eyelids in blinking and sleep ○ ● Eyelids are more forcibly brought together by orbital part (peripherally located) to protect from intense light or foreign bodies Corrugator supercilii - lies deep to orbicularis oculi and frontalis muscles, draws eyebrows medially and produces vertical wrinkles in supranasal part of forehead Muscle of the Face Muscle of the nose: ● ● Procerus - located over the root of the nose, produces transverse wrinkles across the root of the nose Nasalis - transverse and alar parts dilate the nasal aperture (the nose is flattened and widened) Muscles of the mouth: ● Orbicularis oris - fibers encircle oral orifice within substance of the lips. Most fibers are derived from the buccinator and other muscles around the mouth, acting as a sphincter muscle of the lips to compress them together and protrude them Muscle of the Face Muscles of the mouth: ● ● ● ● ● ● ● ● Levator labii superioris Levator anguli oris Zygomaticus minor - elevates upper lip Zygomaticus major - draws angle of mouth upward and backward (smiling) Risorius - retracts angle of mouth (grinning) Depressor anguli oris Depressor labii inferioris Mentalis - draws up and puckers skin of chin (assists in protrusion and eversion of lower lip) Muscle of the Face Buccinator: ● ● ● ● Originates from outer surfaces of alveolar processes of maxilla and mandible, opposite molar teeth, and from pterygomandibular raphe (thin fibrous band that extends from pterygoid hamulus to posterior end of mylohyoid line of mandible) Muscle fibers pass forward and form muscle layer of cheek at angle of the mouth; fibers enter upper and lower lips and become continuous with orbicularis oris Pierced by parotid duct Compresses cheek against molar teeth (aids in mastication, together with tongue, by pushing food between teeth); assists in expelling air from oral cavity (whistling, blowing, playing wind instruments) Innervation of Mimetic Muscles Facial nerve: ● ● Leaves cranial cavity via internal acoustic meatus at lateral end of meatus; enters facial canal (bony canal within petrous part of temporal bone), exits temporal bone via stylomastoid foramen enters parotid gland and passes forward within it (superficial to retromandibular vein and external carotid artery); divides into terminal branches within parotid gland Two groups of branches: ○ ○ Intrapetrosal (branches that facial nerve gives off within facial canal) Extrapetrosal (branches facial nerve gives off distal to stylomastoid foramen). Skin and Scalp